1. Field of the Invention
The present invention relates to immersion lithography, more particularly, to providing methods for insitu lens cleaning in immersion lithography systems.
2. Related Art
Lithography is a process used to create features on the surface of substrates. Such substrates can include those used in the manufacture of flat panel displays (e.g., liquid crystal displays), semiconductor wafers, circuit boards, various integrated circuits, print heads, macro/nano-fluidic substrates, and the like. During lithography, a substrate, which is disposed on a substrate stage, is exposed to an image projected onto the surface of the substrate by exposure optics located within a lithography apparatus.
The projected image produces changes in the characteristics of a layer, for example, photoresist, deposited on the surface of the substrate. These changes correspond to the features projected onto the substrate during exposure. Subsequent to exposure, the layer can be etched or otherwise processed to produce a patterned layer. The pattern corresponds to those features projected onto the substrate during exposure. The patterned layer is then used to remove or further process exposed portions of underlying structural layers within the substrate, such as conductive, semiconductive, or insulative layers. This process is repeated, together with other steps, until the desired features have been formed on the surface, or in various layers, of the substrate.
In the field of immersion lithography the exposure operation is conducted with an immersion liquid, which typically has been water, between the last lens element of the projection optics and the substrate. The surface of the final lens element is manually cleaned periodically using solvents. The residues that are removed are generally from processing associated with resist leaching from the ultra-violet exposure of photoresist on substrates being processed. This approach to lens cleaning is time consuming, as the lens must typically be removed. Moreover, the approach is not well suited for new immersion lithography exposure systems. New immersion lithography systems use high refractive index immersion fluids. The high refractive index immersion fluids are organic and breakdown under ultraviolet exposure to produce carbonaceous deposits, which are not easily manually cleaned from the surface of lens.
What are needed are methods for insitu cleaning of lens used in immersion lithography systems operated with high refractive index immersion fluids.